Data Topic Flashcards
(27 cards)
Systemic random sampling is . . .
The sample is chosen by picking every nth person/item
For example: you pick a person/item at random from your population, then select every nth (maybe 10, 6 any number within reason) after that until you have enough for you sample
Simple random sampling is. . .
Each person/item in the population has a fair chance
For example: make a list of all your people/items in your population, assign them a number/put their names in a hat, and select ones at random until you have enough for your sample size
Stratified random sampling is. . .
The sample is divided up into groups that exist in the same proportion as in the whole population.
For example: if 38% of the entire population are girls, and 62% are boys, then the proportions have to be the same in your sample. So in your sample, 38% would have to be girls, and 62% would have to be boys. Select appropriate numbers from each group at random using the simple random sampling technique.
Advantages and disadvantages of Systematic random sampling are. . .
Advantage:
Easy for surveys/questionaires in real time
Disadvantages:
Everyone/thing in the population doesn’t have an equal chance so the sample could be bias
Advantages and disadvantages of Simple random sampling are. . .
Advantages:
Everyone/thing in the population has a fair chance of selection.
Disadvantages:
Could still give unrepresentative data if the random selects more from a particular group in the population.
Advantages and disadvantages of Stratified random sampling are. . .
Advantages:
All groups in the population would be fairly represented in the sample.
Disadvantages:
Can be time-consuming and complex to find out how to divide the population.
A sample is . . .
A sample is a smaller group within the population that you conduct your investigation on
The population is. . .
The entire group of people/items that you want to find out data of
2 important things to remember when sampling are. . .
1) Samples must be representative/unbiased for the whole population.
2) The larger the sample size, the more accurate it will be. A decent size (or minimum) is 10% of the population.
What are the stages for Stratified random sampling?
1) Check the total is indeed the population
2) Draw the pictures and work out what you times the sample by to get to the population
3) Once that is found, divide all the categories by that value to get how many of each category should be included in the sample.
What do you do is your amount of people/items from Stratified random sampling are decimal?
You round them to make whole numbers
What do you do when asked to compare distribution?
Compare the two ranges, and medians
Point, Explain what this means, Point, Explain what this means - PEPE
If the boys median is bigger …
On average the data is higher
If the boys range is bigger …
On average, the data is more spread out
Using the entire population in sampling is called …
A census
What’s the maximum ‘leyway’ in a pie chart?
2°
How do you calculate how many degrees per person in a pie chart? (From a frequency table)
Add up the frequencies, and do 360 ÷ (frequency total)
That is the number of degrees per person
Then just times the number of degrees per person by the frequency for each category.
Check they all add up to 360
How do you get from the number of degrees in a pie chart, to the number of people/items in that category?
Do 360 ÷ (the total number of people represented in the pie chart)
Keep this as a fraction
Do the number of degrees of each category ÷ (the fraction)
Once this is complete, total up the number of people from each category to check it totals to the number there should be
How do you rearrange the equation for the mean?
You would change it from:
Mean = total ÷ how many things there are
To:
Total = mean x how many things there are
(Use a triangle if necassery)
What’s the MIDPOINT?
The MIDPOINT is the middle point of the grouped category in grouped data
How do you calculate the FX column?
Frequency column x MIDPOINT
How do you calculate the mean of a grouped data frequency table?
Mean = FX column total ÷ frequency column total
How do you work out the modal class?
The class that has the highest frequency
How do you calculate the median class?
The class that contains the middle number The frequency total plus 1, then divide by 2 Then find the class that contains that number
